Bug 1907001 - Add MOZ_HAS_CLANG_ATTRIBUTE r=glandium

Note this patch was provided by a contributor to fix MSVC builds of a SpiderMonkey embedding.

Differential Revision: https://phabricator.services.mozilla.com/D216843

mfbt/Attributes.h

@@ -78,6 +78,13 @@
 #  define MOZ_HAVE_NO_STACK_PROTECTOR __attribute__((no_stack_protector))
 #endif
 
+/* if defined(__clang__) && __has_attribute (attr) may not be portable */
+#if defined(__clang__)
+#  define MOZ_HAS_CLANG_ATTRIBUTE(attr) __has_attribute(attr)
+#else
+#  define MOZ_HAS_CLANG_ATTRIBUTE(attr) 0
+#endif
+
 /*
  * When built with clang analyzer (a.k.a scan-build), define MOZ_HAVE_NORETURN
  * to mark some false positives
@@ -88,15 +95,13 @@
 #  endif
 #endif
 
-#if defined(__GNUC__) || \
-    (defined(__clang__) && __has_attribute(no_profile_instrument_function))
+#if defined(__GNUC__) || MOZ_HAS_CLANG_ATTRIBUTE(no_profile_instrument_function)
 #  define MOZ_NOPROFILE __attribute__((no_profile_instrument_function))
 #else
 #  define MOZ_NOPROFILE
 #endif
 
-#if defined(__GNUC__) || \
-    (defined(__clang__) && __has_attribute(no_instrument_function))
+#if defined(__GNUC__) || (MOZ_HAS_CLANG_ATTRIBUTE(no_instrument_function))
 #  define MOZ_NOINSTRUMENT __attribute__((no_instrument_function))
 #else
 #  define MOZ_NOINSTRUMENT
@@ -121,7 +126,7 @@
  *
  * This is useful to have clearer information on assertion failures.
  */
-#if defined(__clang__) && __has_attribute(nomerge)
+#if MOZ_HAS_CLANG_ATTRIBUTE(nomerge)
 #  define MOZ_NOMERGE __attribute__((nomerge))
 #else
 #  define MOZ_NOMERGE